Although the burner of the present invention is suitable for use in a number of different furnaces, it will be described for illustrative purposes embodied in a launder, such as one used to convey molten brass from a melting furnace to a holding furnace and automatic casting machine.
Known launders conventionally use a plurality of gun type burners which shoot a high velocity flame onto the surface of the flowing molten metal. These burners not only consume relatively large quantities of fuel, but also, because of the direct impingement of the flame upon the surface of the molten metal, cause the latter to oxidize and/or constituents of an alloy to be burned out. Furthermore, this direct impingement causes erosion of the refractory lining, which results in pockets being formed therein in which pools of molten metal collect at the end of a run, the metal in these pools being further oxidized and/or burned by the flames so that they contaminate the next run. In addition, most launders are so constructed that they must be run twenty-four hours a day because it would take too long to bring them up to temperature at the beginning of a day.
The burner of the present invention has as its object overcoming these disadvantages of known burners, in launders as well as other furnaces which suffer from the same problems. This is accomplished by utilizing a relatively narrow strip of porous refractory material which breaks the flame up into a large number of relatively small low-velocity flames which are spread over a strip of finite width which extends for substantially the full extent of the combustion chamber in at least one direction. The heat is therefore very evenly distributed. Because of the reduced velocity there is no undesirable impingement of the flame directly on the molten metal, and furthermore the heat of combustion is retained in the furnace for a longer time than with high velocity gun type burners (which force a great deal of heat up the stack), thus permitting the heated material to absorb more of the heat generated by a unit of fuel, whereby thermal efficiency is increased and fuel consumption reduced. The present invention has as a further object the provision of an improved launder construction, and one which can be turned off at night, thus reducing fuel consumption, fire hazard, insurance rates and the like.
Another object of the present invention resides in the provision of an improved burner which itself receives maximized cooling, by having a minimum of surface area exposed to the radiant and convective heat in the combustion chamber, thus improving reliability and life. A related object concerns the provision of such a burner which has a relatively large dimension in the direction of fuel flow, whereby flash backs are prevented and thorough fuel/air mixing is insured.
Another object of the present invention resides in the provision of an improved porous refractory type burner which does not require special surface treatment to increase the reflectivity and reduce the heat absorption qualities thereof, thus facilitating cooling and reducing the production of infra red radiation.
Another object of the present invention resides in the provision of a furnace having a minimum surface area in the combustion chamber, whereby the degree of heating by convection is increased and amount of radiation is reduced, whereby thermal efficiency is improved.
Another object of the present invention resides in the provision of a furnace which does not require the use of excess air for solely cooling purposes.